Injection moulding

ABSTRACT

A process for the manufacture of thin-walled articles comprising the steps of: 1) selecting a polymer blend having an ESCR of greater than 10 hours; i) a plurality (preferably 6 or more) of strips of the polymer blend incorporating any post molding treatment intended for the final article having the cross-sectional dimensions of 0.65 mm in thickness and 10 mm in width are injection molded under high shear, long flow length conditions, similar to those intended for use in the manufacture of the flexible thin-walled article; ii) the strips are bent back upon themselves and stapled 3 mm from the bend; iii) the bent strips are immersed in a solution of a stress crack agent and held at a temperature of 50° C.; iv) the strips are observed for signs of cracking, any signs of cracking are regarded as a failure; and v) the time to failure is when 50% of the strips show signs of cracking; 2) melting said polymer blend; 3) ramming the molten polymer blend into a mold, said mold having a cavity which produces a thin-walled article having a thin section less than 1 mm in thickness and wherein the thin section is substantially continuous for greater than 50 mm in the direction of flow of the molten polymer blend in the mold; and 4) removing from the mold the thin-walled article formed from the polymer blend.

FIELD OF THE INVENTION

The present invention relates to injection moulding processes, inparticular to a process for injection moulding articles having thinsections such as thin-walled tubular containers as used in the cosmeticsindustry for lotions, moisturisers and the like.

FIELD OF INVENTION

Thin-walled tubular containers, such as those used in the cosmeticsindustry, are currently produced by a combination of extrusion,injection moulding and welding processes (generally referred to hereinas the extrusion process). The body of the tube is extruded in the formof a continuous cylinder which is then cut into the desired length toform the body of the container. In a separate injection moulding processthe “head and shoulders” of the tube are produced. The injection moulded“head and shoulders” are then welded to the extruded tube to form thecontainer. Once the container is filled with product the tail end of thecontainer is sealed by a further welding process. This process forproducing tubes has a number of limitations, the main being the highequipment cost, the lack of variety of tube shapes that can be producedusing it, no ability to provide various textured surface finishes orembossing as an integral part of the manufacturing process, and noability to incorporate attachments/components such as closures and hooksduring the manufacturing process. Low MFI polyethylene (MFI generallyless than 2) is the preferred polymer for tube manufacture as it ingeneral imparts the properties of good feel and flexibility required bycustomers and is suitable for extrusion processing. In addition, low MFIpolyethylene offers sufficient product resistance and barrier propertiesto make it suitable for most products currently packed into tubes. Incases where the barrier properties of polyethylene are inadequate forparticular applications, medium density polyethylene (MDPE), highdensity polyethylene (HDPE), polypropylene (PP) and multilayerpolymerfilms are commonly used.

While the injection moulding of articles such as thin walled containershas been proposed, it has hitherto not been possible to injection mouldsuch articles having relatively long, thin sections without the articlesbeing too susceptible to failure to be of commercial or practical use.The main problems have been associated with the polymers used toinjection mould tubes, in that the process of moulding a cylindrical orother shaped tube requires the polymer to simultaneously have a high MFIto enable said polymer to flow down the long, narrow and curved pathdictated by the tube shape without the use of excessive injectionpressures, yet to have sufficiently good mechanical properties to beable to withstand handling and resist the stress cracking effects ofmany of the products that will be packed in it. In order to injectionmould a tube, conventional techniques would require the polymer to haveflow properties capable of forming moulded parts with radii and alength/thickness ratio of 100 and often higher. Forcing a ‘standard’polymer to flow in a mould with such dimensions introduces severestresses into the polymer, these stresses being “frozen” into thearticle thus produced when the polymer rapidly cools below itscrystallising temperature before these stresses can be relieved. Thesestresses result in the tube having surprising different and deterioratedproperties relative to the other products moulded from the same polymersunder less severe moulding conditions.

Further stresses are introduced into the tubes when they are filled withproduct and then crimped d sealed—most often by heat sealing orultrasonic welding. This process involves bending the ‘open’ end of thetube back on itself through an angle of up to 180° to form the fold atthe edge of the seal. This fold is in the direction of the flow of thepolymer, which direction having been demonstrated to be the direction ofmaximum weakness of the moulded product. This ‘folded and sealed’ area,where the tube is required to be deformed in order to effect a seal, isan area of the injection-moulded tube particularly susceptible to stressand flex cracking.

The following examples illustrate the special problems of injectionmoulding such tubes. Tubes were injection moulded using DuPont 2020Tpolymer, a polymer DuPont describe as “especially suited for injectionmoulded closure and extruded tubing where flexibility and maximumresistance to environmental stress cracking is required”. These tubeswere moulded with extreme difficulty, requiring very high injectionpressures and temperatures simply to get the 2020T to fill the mould. Ineach moulding significant degrees of core shifting/flexing were noted,due no doubt to the extremely high injection pressures that wererequired. In addition, it was noted that the tubes had virtually noresistance to flexing in the direction of the material flow, withsignificant cracking being induced with less than 5 manual squeezes ofthe tube. The environmental stress cracking of the same tubes wastested, and in spite of claims of “maximum resistance” to environmentalstress cracking, was found to be totally inadequate for mouldingthin-walled tubes by injection moulding.

In another illustration of the difficulty of injection moulding tubes, aDow ‘Dowlex’ LLDPE pamphlet advises that LLDPE has substantially betterESCR properties than an equivalent high pressure LDPE. To illustrate thedifference, the pamphlet states that in one comparative test a high DowDowlex LLDPE has an ESCR in oil some 80 times better than that achievedby a high pressure LDPE with the similar density and MFI (5700 hrscompared to 70 hrs). It further states that the LLDPE has an ESCRapproximately 10 times better than the LDPE when immersed in a 10% Tericsolution at 50° C. (225 hrs vs 26 hrs). However, contrary ro theseobservations, we have found that when these polymers are moulded in theform of thin-walled tubes and ESCR subsequently tested using a speciallydesigned test method for assessing tube ESCR, both Dow's ‘Dowlex’ LLDPE2517 and Kemcor's LD 8153 (a high pressure LDPE with similar MFI anddensity) performed poorly in 10% Teric N9 at 50° C., and both failedwithin 20 minutes—clearly indicating their unsuitability for tubemanufacture by injection moulding. This poor result is illustrative ofthe highly unusual and difficult nature of manufacturing injectionmoulded thin-walled tubes acceptable to the market.

SUMMARY OF THE INVENTION

We have now found that it is possible to injection mould flexiblethin-walled articles having relatively long thin-walled sections byselection of the polymers used in the injection moulding process havinga time to failure of greater than 10 hours when tested according to thefollowing procedure:

i) a plurality (preferably 6 or more) of strips of the polymer blendincorporating any post moulding treatment intended for the final articlehaving cross-sectional dimensions of 0.65 mm in thickness and 10 mm inwidth are injection moulded under high shear, long flow lengthconditions, similar to those intended for use in the manufacture of theflexible thin-walled article.;

ii) the strips are bent back upon themselves and stapled 3 mm from thebend;

iii) the bent strips are immersed in a solution of a stress crack agentsuch as an ethoxylated nonylphenol, eg. a 10% solution of Teric N9(nonylphenol ethoxylated with 9 moles of ethylene oxide—Orica AustraliaPty Ltd) and held at a temperature of 50° C.;

iv) the strips are observed for signs of cracking; and

v) the time to failure is when 50% of the strips show signs of cracking.

Any reference to “an ESCR” throughout the specification and claims whichfollow, unless specfically stated otherwise, refers to an ESCRdetermined using the above test procedure. Accordingly, the inventionprovides a process for the manufacture of thin-walled articlescomprising the steps of:

1) selecting a polymer blend having an ESCR of greater than 10 hours;

2) melting the polymer blend;

3) ramming the molten polymer blend into a mould having a cavity whichproduces a thin-walled article having a thin section of 1 mm or less inthickness and wherein the thin section is substantially continuous forgreater than 50 mm in the direction of flow of the molten polymer blendin the mould; and

4) removing from the mould the thin-walled article formed from thepolymer blend.

By “substantially continuous”, it will be understood by those skilled inthe art that the thickness of the thin section is generally maintainedat of 1 mm or less although some variation resulting in an increase inthickness is permitted, for example when an embossed, textured or relieffinish is incorporated into that article. The thickness refers to thethickness of the layer of polymer blend described above and excludes anyadditional layers such as may be incorporated as a multilaminate. Inapplications where the blend is foamed we refer to the notionalthickness of an unfoamed material which can be readily determined fromthe density of the polymer blend.

It will be understood that throughout the specification and claims whichfollow, the term “polymer blend” refers to compositions comprising atleast one polymer and optionally incorporating additional componentssuch as are described herein.

It will be understood that throughout the specification and claims whichfollow, the term “copolymer” refers to polymers incorporating two ormore monomer units therein.

The polymer blends selected for the manufacture of flexible thin-walledarticles according to the invention have an ESCR of greater than 10hours. Preferably the ESCR of the polymer blend is greater than 100hours, more preferably greater than 200 hours and most preferablygreater than 360 hours. Where the flexible article is a tube or othercontainer used for the packaging of a composition such as a moisturiseror a shampoo which may be quite aggressive to the thin walled articleand result in a degradation of its properties over time, it is desirableto select a polymer blend having an ESCR sufficiently high such that thethin walled article formed from the blend is able to withstand therigours of use despite any degradation of properties resulting from theaggressive nature of the materials contained within the thin-walledarticle. Where the thin-walled article is used for the packaging of arelatively inert material, a lower ESCR may be tolerated.

The ESCR test as hereinabove defined may be conducted using a variety ofstress crack agents. The preferred stress crack agent is Teric N9,although other ethoxylates of nonylphenol may also advantageously beused. Other stress crack agents may also be used and may be selectedbased upon the desired end-use. For example, other stress crack agentsmay include mineral oils, cationic surfactants, solvents and otheragents which will be apparent to those skilled in the art.

Advantageously, the ESCR test as described above is conducted undermoulding conditions similar to those to be used in the manufacture ofthin-walled articles. For example where it is intended to produce thethin-walled article using a moulding incorporating melt flow oscillationtechniques, it is advantageous to conduct the ESCR tests on panelsproduced from mouldings made by employing melt flow oscillationtechniques.

The ESCR test as described herein has allowed a variety of polymerblends to be identified which are able to be injection moulded to formthin-walled articles. In a second aspect of the present invention thereis provided a process for injection moulding a thin-walled articlecomprising the steps of:

1) melting a polymer blend having an ESCR of greater than 10 hours, saidpolymer blend comprising at least one polymer and at least onecompatible agent and/or at least one nucleating agent;

2) ramming the molten polymer blend into a mould said mould having acavity which produces a thin-walled article having a thin section lessthan 1 mm in thickness and wherein the thin section is substantiallycontinuous for greater than 50 mm in the direction of flow of the moltenpolymer blend in the mould; and

3) removing from the mould the thin-walled article formed from thepolymer blend.

A wide variety of polymers may be used as the base of a blend whichmeets the ESCR test as hereinabove defined or acts as the at least onepolymer in the second aspect of the present invention. These polymersinclude olefin homopolymers and copolymers, preferably ethylene orpolypropylene homopolymers and copolymers with C₃-C₂₀ alpha or betaolefins and/or polyenes, preferably C₃-C_(x) alpha or beta olefins, suchpolymers having densities ranging from very low to high density (densityranges between 0.85 and 0.97 g/cm³). Also suitable for use in thepresent invention are ethylene, propylene and butene copolymers withterminal vinyl groups and ethylene, propylene and butene copolymerscontaining greater than 50% ethylene, propylene or butene which arecopolymerised with comonomers such as methyl acrylates, ethyl acrylates,acrylic acid and methacrylic acid, ionomers, andstyrene-ethylene/butene-styrene ABA copolymers. These polymers may bemade by a wide variety of methods including high and low pressureprocesses, using a wide variety of catalysts such as Ziegler-Natta andmetallocenes, and have molecular structures ranging from linear tohighly branched, thus included are LDPE, MDPE ant HDPE. Particularlysuitable for use in the present invention are plastomers, ‘substantiallylinear’ and branched polyethylenes or polypropylenes, copolymers ofpropylene and ethylene or one or more alpha-olefins, terpolymers ofethylene, propylene and one or more alpha-olefin (of which Montell'sCatalloy polymers are an example) and polymers and copolymers ofpropylene manufactured using metallocene catalysts. Other polymorssuitable for use in the present invention include polylactic acidpolymers.

We have found that plastomers, ‘substantially linear polyethylenes’,metallocene branched polyethylene copolymers, propylene alpha-olefininterpolymers and metallocene propylene polymers and interpolymers arepreferred for use in the present invention for the production ofthin-walled products, and especially for the production of flexibletubes. A key characteristic of plastomers, ‘substantially linearpolyethylenes’, metallocene branched polyethylene copolymers, propylenealpha-olefin interpolymers and metallocene propylene polymers andinterpolymers is their composition distribution i.e. the uniformity ofdistribution of comonomer within and among the molecules of the polymer.Plastomers, ‘substantially linear polyethylenes’, metallocene branchedpolyethylene copolymers, propylene alpha-olefin interpolymers andmetallocene propylene polymers and interpolymers are generally madeusing metallocene catalysts, which are known to incorporate comonomervery evenly among and along the polymer molecules they produce. Thusmost molecules of a particular plastomer, ‘substantially linearpolyethylenes’, metallocene branched polyethylene copolymers, propylenealpha-olefin interpolymers and metallocene propylene polymers andinterpolymers will have roughly the same comonomer content, and withineach molecule the comonomer will be super-randomly distributed.Ziegler-Natta catalysts generally yield copolymers having a considerablybroader composition distribution—specifically the comonomer distributionin polymers thus produced will vary widely among the polymer molecules,and will also be less randomly distributed within a given molecule.

U.S. Pat. No. 5,451,450, the disclosures of which are hereinincorporated by reference, describes plastomers as ethylene alpha-olefincopolymers (including ethylene/alpha-olefin/polyene copolymers) with amolecular weight distribution in a ratio M_(w)/M_(n) range of 1.5-30,preferably in the range of 1.8-10 and more preferably in the range 2-4.Generally, plastomer polymers comprise ethylene homopolymers andinterpolymers of ethylene, with at least one C₃-C₂₀ α-olefin copolymerbeing especially preferred. The term “interpolymer” is used herein toindicate a copolymer or a terpolymer or the like. That is, at least oneother comonomer is copolymerised with ethylene to make the interpolymer.Generally the α-olefins suitable for copolymerisation with ethylene toform plastomers contain in the range of about 2 to about 20 carbonatoms, preferably in the range of about 3-16 carbons, most preferably inthe range of about 3-8 carbon atoms. Illustrative non-limiting examplesof such α-olefins are propylene, 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene, and 1-dodecene and the like.Polyene comonomers suitable for the copolymerisation with ethylene toform plastomers suitable for the present invention have, in the main,about 3 to 20 carbon atoms, preferably in the range of about 4 to about20 carbon atoms, most preferably in the range of about 4 to about 15carbon atoms. In one embodiment the polyene is a diene that has in therange of about 3 to about 20 carbon atoms, and may be a straightchained, branched chained or cyclic hydrocarbon diene. Preferably thediene is a non-conjugated diene. Non-limiting examples ofethylene/alpha-olefin plastomers suitable for the present inventioninclude ethylene/butane-1, ethylene/hexene-1, ethylene/octane-1 andethylene/propylene copolymers. Non-limiting examples of terpolymerplastomers suitable for the present invention includeethylene/propylene/1,4 hexediene and ethylene/octene-1/1,4 hexediene.

Plastomers and ‘substantially linear polyethylenes’ are produced mainlywith the use of metallocene catalysts. U.S. Pat. No. 5,281,679, thedisclosures of which are herein incorporated by reference, shows amethod of producing metallocene homo and copolymers with a broadmolecular weight distribution, generally in the range of 3-30, whichhave improved tensile and impact strength relative to Ziegler-typecatalysed polymers. They are also characterised by having considerablynarrower short chain branching distributions, and lower hexaneextractables. Such polymers are suitable for use in the presentinvention.

In germs of densities, the plastomers preferred for use in the processof the present invention are comparable to VLDPE or ULDPE, which arealso copolymers of ethylene with α-olefins, such as butene, hexene oroctene. They are generally defined as ethylene alpha-olefin copolymerswith densities between 0.86 and about 0.915. The process for makingVLDPEs is generally described in EP 120503. Plastomers, even those withthe same density as VLDPEs, have greatly different physical propertiesdue to differences in the manufacturing process—primanly in the use ofmetallocene catalysts. In general, a VLDPE compared to a plastomer ofsimilar density has a significantly higher melting point and softeningpoint, molecular weight/size distribution higher than 3 and a higherlevel of crystallinity.

Elastic substantially linear olefin polymers as disclosed in a number ofpatents including U.S. Pat. No. 5,272,236, U.S. Pat. No. 5,278,212, U.S.Pat. No. 5,380,810, U.S. Pat. No. 5,525,695 and U.S. Pat. No. 5,665,800all of which are incorporated herein by reference. As an example of anelastic substantially linear olefin polymer, U.S. Pat. No. 5,578,272describes one type as having have a critical shear rate at onset ofsurface melt fracture of at least 50% greater than the critical shearrate at onset of surface melt fracture of an olefin polymer having thesame I₂ and M_(w)/M_(n). These polymers also have a processing index(PI) less than or equal to a comparative linear olefin polymer ae thesame I2 and M_(w)/M_(n). Elastic substantially linear polymerscomprising ethylene homopolymers and interpolymers of ethylene with atleast one C₃-C₂₀ α-olefin copolymers are especially preferred. The term“interpolymer” is used herein to indicate a copolymer or a ter polymeror the like. That is, at least one other comonomer is copolymerised withethylene to make the interpolymer.

The term ‘substantially linear’ polymers means that the polymer backboneis substituted with about 0.01 to about 3 long chain branches per 1000carbons, most preferably 0.03 to 1 long chain branches per 1000 carbons.The term “linear olefin polymer” means that the polymer does not havelong-chain branches, as for example the traditional linear low densitypolyethylene or linear high density polyethylene polymers made usingZiegler polymerisation processes (e.g. U.S. Pat. Nos. 4,076,698 and3,645,992), the disclosures of which are incorporated herein byreference.

The SCBDI (short chain branch distribution index) is defined as theweight percent of molecules having a comonomer contem within 15% of themedian total molar comonomer content. The SCBDI of the substantiallylinear polymers suitable for the present invention is preferably greaterthan about 30%, and especially greater than about 50%.

A unique characteristic of the mbstantially linear polymems of thepresent invention is a highly unexpected flow property where the I₁₀/I₂value is essentially independent of polydispersity index (i.e.M_(w)/M_(n)). This is contrasted with conventional polyethylene resinshaving rheological properties such as the polydispersity index, theI₁₀/I₂, increases. The density of the ethylene or ethylene/α-olefinsubstantially linear olefin polymers in the present invention isgenerally from about 0.85 g/cm³ to about 0.97 g/cm³, preferably fromabout 0.85 to 0.92 g/cm³.

The substantially linear polymers preferred for use in the process ofthe present invention have processability substantially similar to thatof high pressure LDPE, while possessing the strength and other physicalproperties similar to those of conventional LLDPE without the benefit ofspecial adhesion promoters (e.g. processing additives such as Vitonflouroelastomers made by DuPont).

U.S. Pat. No. 5,525,695 (the disclosures of which are hereinincorporated by reference) describes a manufacturing method for‘substantially linear polyethylenes’, and characterises them as having:

A. a density from about 0.85 g/cm³ to about 0.97 g/cm³;

B. an MI from 0.01 g/10 min to 1000 g/10 min;

C. and preferably a melt flow ratio of I₁₀/I₂ from about 7 to 20; and

D. a molecular weight distribution M_(w)/M_(n) preferably less than 5,especially less than 3.5 and most preferably from about 1.5 to 2.5.

Elastic substandally linear olefin polymers can be made with broadermolecular weight distributions by means of the appropriate selection ofcatalysts for the polymerisation process as described in U.S. Pat. No.5,278,272. Broader MWD material exhibits a higher shear rate or shearstress dependency. In other words, generally the broader the MWD, thehigher the effective MFI at high shear, and hence the better theprocessing characteristics. Broad molecular weight ‘substantially linearolefin polymers’, plastomers and metallocene branched polyethylenes areparticularly suited to the production of tubes by the process of thepresent invention.

Further, we have found that some types of polymers, preferablyunsaturated polymers such as polyvinyl chloride and polystyrene, morepreferably polyolefins and even more preferably plastomers,‘substantially linear polyethylene’, metallocene branched polyethyleneand polypropylene copolymers and most preferably plastomers and‘substantially linear polyethylene’ polymers and polypropylenecopolymers having densities between 0.87 and 0.92 and MFIs above 10,preferably above 20 and most preferably above 30 may, with the additiononly of nucleating agents as a means of improving the ESCR of the tubes,be used to produce tubes suitable for packaging some less aggressiveproducts. However, the addition of comparible polymers such aspolypropylene and polypropylene copolymers to such polymers in additionto the nucleating agents results in better overall ESCR resistance, andare generally preferred.

It has been established that polymers, but particularly plastomers andsubstantially linear olefins, having higher-than-normal I₁₀/I₂ valueswhuch are essentially independent of polydispersity index (i.e.M_(w)/M_(n),) and metallocene polypropylene homo and copolymers areparticularly suited to the manufacture of injection moulded tubes andother thin-walled articles having good ESCR and other physical/chemicalproperties. As discussed in U.S. Pat. No. 5,281,679 the disclosures ofwhich are incorporated herein by reference, broadening the molecularweight distribution of a polymer—and particularly polyethylene and itscopolymers—increases the rensile strength and impact strength ofproducts made therefrom. The main reason for high I₁₀/I₂ in a polymer isthe presence of both high MW and low MW molecules in the polymer. It isbelieved that the high MW molecular fraction contribute significantly toimproving the ESCR properties of the polymer, while the low MW molecularfraction contnbute to the improved processability of the polymer byincreasing the shear sensitivity of the polymer, thereby enabling thepolymer to be molded into tubes in spire of the apparently low MFI(usually measured as I₂) of the polymer.

High I₁₀/I₂ polymers suitable for the present invention may be producedby a variety of methods. These include:

1) intimately blending two or more polymers having different molecularweights in appropriate blending equipment;

2) producing bi or multi modal polymers with high I₁₀/I₂ by means of‘tandem’ reactors; and

3) producing bi or muld modal polymers with high I₁₀/I₂ in a singlereactor using appropriate catalysts.

The catalysts used to produce bi or multi modal polymers with highI₁₀/I₂ may be selected to produce:

1) broad molecular weight distribution polymers (ea. with molecularweight distribution in the 3-30 range as described in U.S. Pat. No.5,281,679 which is incorporated herein by reference); or

2) effectively two or more polymers, each having either a narrow orbroad molecular weight distribution as desired. U.S. Pat. No. 5,539,076the disclosures of which are herein incorporated by reference, describesa method of manufacturing bi or multi modal polyethylene polymers withdensities between 0.89 and 0.97 in a single reactor.

Other polymers suitable for injection mouiding tubes are silane-graftedor copolymerised polymers. Such polymers can be crosslinkedpost-processing, resulting in mouldable/processable, crosslinked polymercompounds which provide the ease of processability and design/processflexibility of relatively low viscosity polymers while achieving thestrength and other benefits of higher viscosity, cross-linked polymersand copolymers. These polymers also eliminate the need for prolongedcycle times and elevated temperatures to achieve in-mould crosslinking.There are numerous patents describing various aspects of the method ofpreparing and crosslinking of various silane-based compositions that canbe used in the present invention. Included are U.S. Pat. Nos. 5,055,249,4,117,063, 4,111,195, 4,413,066, 4,975,488 and 3,646,155, thedisclosures of which are incorporated by reference.

In a further aspect of the present invention there is provided acompound in which all the ingredients can be mixed in a single step inan extruder immediately prior ro injection moulding. The compoundconsists of one or more polymer types, such as acrylates or branchedmetallocene-catalysed ethylene alpha-olefin plasromers which is reactedwith an organosilane compound such as vinyl trimethoxy silane in thepresence of a peroxide, such as dicumyi peroxide, to produce asilane-grafted polymer - this reactive processing taking place in thebarrel of an injection moulder. Then, just prior to injecting the silanegrafted polymer into a mould, a catalyst such as dibutyl tin dilaurateis introduced into the silane grafted polymer in the barrel of themoulder and mixed to ensure intimate mixing of the catalyst and thegrafted polymer. The catalyst facilitates the post-moulding crosslinkingof the silane components on the polymer backbone in the presence ofmoisture by means of condensing the hydrolysable silane groups ondifferent polymer backbones, thus producing a new polymer which hasproperties that are a combination of the properties ofrhe individualpolymers from which the silane-grafted polymers have been produced aswell as the properties conferred by the higher molecular weight polymermolecules that result from the above crosslinlcing. The final properriesof the new polymer can be varied by changing the proportions of thevarious polymers, varying the nature of either or both polymers (ea. byusing polymers with additional fictional groups such as vinyl acetateand/or varying the properties of the silane-containing polymer by, forexample, changing the type of polyethylene and/or silane type chemicallybound to a polymer). The final properties can further be changed by theaddition of other compounds/additives such as fillers, plasticisers andantioxidants that are well known to anyone practiced in the art ofpolymer compounding.

An alternative method of producing silane grafted polymers suitable foruse in the present invention is to graft the silane onto the polymer inthe presence of a peroxide or other free radical generator in a suitablereactor, such as an extruder as a separate step, and to package theresultant grafted polymer in moisture proof packaging for subsequentuse. When desired, the grafted polymer may be introduced into theinjection moulder together with a suitable amount of a condensationcatalyst, the two components being intimately blended together in themoulder, and then injection moulded and cross-linked post-processing.

The silane-containing polymer typically contains between 0.1 and 15% ofhydrolysable silane. The most common hydrolysable silanes used in theproduction of silane-containing polymers are vinyltrimethoxysilane,vinyltriethoxysilane, but can be any hydrolysable silane that can beincorporated into another polymer to form a silane-containing polymer.

The at least one compatible agent is preferably a polymer and whenblended with the at least one polymer results in blends havingproperties which, when blended is used to mould thin-walled articlessuch as flexible injection moulded tubes, are superior to the originalconstituents or the neat polymers. The at least one compatible agent maybe selected from the group consisting of ethylene vinyl acetate;ethylene vinyl alcohol; plasticised polyvinyl acetate and polyvinylalcohol; alkyl carboxyl substituted polyolefins; copolymers ofanhydrides of organic acids; epoxy group containing copolymers;chlorinated polyethylene; ethylene-propylene-butylene etc. copolymers;ultra low density, very low density, low density, medium density andhigh density polyethylene; polypropylene, polybutylene and copolymersthereof; polyester esters; polyether-esters (such as DuPont's Hytrelrange); acrylonitrile-methacrylate copolymers; block copolymers havingsyrene end blocks; half esters; amino and alkoxysilane graftedpolyethylenes; vinyl addition polymers; syrene butadiene blockcopolymers; acid grafted polyolefins; vinyl pyrrolidine graftedpolyolefins; block copolymers of dihydric monomers; propylene graftunsaturated esters; modified polyolefins comprising amide, epoxy,hydroxy or C₂-C₆ acyloxy functional groups other polymericcompatibilisers suitable for use with polyolefins; particles coated withany of the above; and mixtures thereof. In the above compatible agentsthe functional groups are generally incorporated into the modifiedpolyolefin as part of an unsaturated monomer which is eithercopolymerised with an olefin monomer or grafted onto a polyolefin toform the modified polyolefin.

Alkyl carboxyl substituted polyolefins may include substitutedpolyolefins where the carboxyl groups are derived from acids, esters,anhydrides and salts thereof. Carboxylic salts include neutralisedcarboxylic acids and are often referred to as ionomers (ea. Surlyn).Typically acids, anhydrides and esters include methacrylic acid, acrylicacid, ethacrylic acid, glysidyl maleate, 2-hydroxyacrylate, diethylmaleate, maleic anhydride, maleic acid, esters of dicarboxylic acids,etc. Preferred examples include ethylenically unsaturated carboxylicacid copolymers such as polyethylene methacrylic acid and polyethyleneacrylic acid and salts thereof.

Copolymers of anhydrides of organic acids include copolymerb of maleicanhydride as well as copolymers of cyclic anhydrides.

Poly-2-oxazoline compounds and fluoroelastomers are also suited for useas compatible agents. Incorporation of 1-40%, most preferably 2-20% ofpoly-2-oxazoline compounds is preferred. These compatible agents improvethe adhesion of the PE blend to various substrates, which may make themuseful for printing or labelling. The compatibilizing agent comprises analpha-olefin copolymer substrare grafted with amounts of monovinylidenearomatic polymer. Preferably, the alpha-olefin copolymer substrate is aterpolymer of ethylene, propylene and a non-conjugated diolefin.

Many copolymers of ethylene are also useful as compatible agents in theprocess of the present invention. For example single sire catalysedpolymers such a metallocene catalysed polyethylene may be used ascomparible agents in the present invention.

Polypropylene suitable as compatible agents for use in the process ofthe present invention may include isotactic, sydiotactic and attacticpolypropylone and syndiotactic polypropylene of various MFIs, densitiesand crystallinities as would produce desired properties in productsmoulded by the process of the present invention. Particularly whenblended with low molecular weight plastomers, a wide variety ofpolypropylene polymers possessing a very wide range of MFIs (1-200+),densities and crystallinities will produce blends suitable for use inthe process of the present invention.

Polyethylene suitable as compatible agents for use in the process of thepresent invention may include polyethylenes of various MFIs, densitiesand crystallinities as would produce desired properties in productsmoulded by the process of the present invention. Included are very low,low, medium and high density polyethylene, particularly when blendedwith low molecular weight plastomers, substantially linearpolyethylenes, and metallocene branched polyethylene polymers. A widevariery of polyethylene polymers possessing a very wide range of MFIs(1-200+), densines and crystallinities will produce blends suitable foruse in the process of the present invention.

Many monomers have been copolymerized with propylene to form copolymersof propylene. Many of these copolymers are suitable as compatible agentsfor use in the present invention. Examples of ethylene-propylenecopolymers include Montell's SMD6100P, XMA6170P. Further examples ofpolypropylene copolymers are Montell's Catalloy KS-084P andKS-357P—these products are believed to be terpolymers of propylene,ethylene and butene. Other such copolymers and/or terpolymers may beused.

Ionomers provide particular advantages as compatible agents whencombined with plastomers, substantially linear polyethylene, andbranched polyethylenes as the at least one polymer Ionomers aretypically copolymers of ethylene and acrylic or methacrylic acids whichhave been neutralised with metal ions such as sodium, lithium or zinc.One group of ethylene copolymers, called ionomers, are exemplified bythe commercial product Surlyn (manufactured by DuPont). Ionomers tend tobehave similarly to cross linked polymers at ambient temperature, bybeing stiff and tough, yet they can be processed at elevatedtemperatures. The blend of plastomer and ionomer is particularlypreferred, such blends provide polymers with increased barrierproperties.

The block copolymers of dihydric monomers may include block copolymersof dihydric phenol monomers, a carbamate precursor and a polypropyleneoxide resin.

The compatible agent is used in an amount at least sufficient to improvethe environmental stress crack resistance of the polymer blend. Standardtests for environmental stress crack resistance are of little value indetermining how particular polymer blends will perform in rhemanufacture of thin walled articles such as tubes. While not wishing tobe bound by theory it is believed that the injection moulding of thinwalled articles such as tubes introduces and freezes unique stressesinto mouldings. The degree and orientation of stresses in articles suchas injection moulded tubes result in their susceptibility toenvironmental stress cracking. Accordingly, in order to demonstrate theimprovement in environmental stress crack resistance resulting from thepresent invention, the rest hereinabove described was developed

In certain formulations, 2% or less of comparible agent is sufficient toimprove the environmental stress crack resistance of the polymer blendrelative to the environmental stress crack resistance of the plastomer.

The compatible agent may also be used in amounts in excess of thoserequired to compatiblise the polymer blend in order to improve theviscosity characteristics of said polymer blend so as to optimise themoulding characteristics of said polymer blend and/or general propertiesof the moulded product such as softness and flexibility. Typically, thecompatible agent is used in an amount of from about 2 to about 98 weightpercent of the polymer blend, although lower amounts may be used incertain polymer blends. The optimum amount for a specific formulationwill depend on the properties required and can be determined byexperimentation. Further it has been found that inclusion of percentagesof compatible agent that are greater than necessary for increasing theenvironmental stress crack resistance of the polymer blend will oftenalso enable the improvement of the polymer blend properties such as tearand impact strength, barrier properties, chemical resistance, processingand product feel. For example, the incorporation of greater thannecessary percentages of polypropylene to improve the environmentalstress crack resistance of a polyethylene blend to the desired level mayimprove the chemical resistance and reduce the water vapour and watertransmission ratio of the polymer blend compared to polymer blendscontaining the minimum amount of polypropylene required to improve theenvironmental stress crack resistance only. Further, it has been foundthat the inclusion of greater than necessary percentages of compatibleagent may enable the incorporation of greater percentages of otherpolymers than would otherwise be consistent with this invention. Thus,using the compatible agent in such quantities may enable theincorporation of greater-than-otherwise-possible amounrs of suchbeneficial, essentially incompatible other polymers such as nylons andEVOH—with concomitant improvements in properties such as tear and impactstrength, barrier properties, chemical resistance and product feel.

Barrier resins may be incorporated into the polymer blends of thepresent invention. Barrier resins that may be compatibilised with the atleast one polymer include: condensation polymers such as polyamides,polycarbonates and various esters such as polyethylene terephthalate(PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN);polyvinylchloride (PVC); polyvinylidene chloride (PVDC); ethylene vinylalcohol (EVOH); polyvinyl alcohol (PVOH); ethylene vinyl acernre (EVA);EMA, EMAA, EEA; ionomers; monovinylidine aromatic polymers andcopolymers; ethylene, propylene and buylene copolymers; chlorosulfatedpolyethylene, polyisoprene and polychloroprene, polyalkalenephenyleneester and ester ether; phenylfomaldehyde; polyacrylate; polyesterethers; acrylonitrile-methacrylate copolymers; nitrile copolymers;polyacrylonitale; polyurethane and polyaceyls. It will be appreciatedthar certain barrier polymers will be more or less compatible with theat least one polymer than others. For example, EVOH with a sufficientlyhigh ethylene content will be compatible with the at least one polymer,particularly wherein said polymer is an ethylene copolyoner such as aplastomer, while EVOH with a relatively low ethylene content will beessentially incompatible. Barrier properties of the polymer blends ofthe present invention may be further enhanced by the addition ofadditives capable of reacting with or absorbing deleterious chemicalssuch as oxygen and other gases.

The polymer blend may also incorporate a variety of other additives.Examples of additional additives include further polymers, pigments,dyes, fillers, antioxidants, plasticisers, UV protection, viscositymodifying agents, additives capable of reacting with or absorbingdeleterious chemicals such as oxygen and other mould release agents andmelt strength modifiers amongst others. These additives may be added toone or more components of the polymer blend or the polymer blend as awhole prior to moulding in order to modify its properties to suitspecific applications or to achieve specific effects in the end product.

In order to obtain the desirable barrier properties using an essentiallyincompatible polymer and without preorientation of the polymers prior toinjection moulding it is preferred that the melt flow index of thedisperse phase should be somewhat greater than the melt flow index ofthe continuous phase ar the same shear rate. In particular, the barrierresin (usually the disperse phase) preferably has a melt flow index inthe range of from 1.1 to 3.5 times greater than the melt flow index ofthe continuous phase. For optimum barrier properties it is believed thatthe disperse phase droplets should distort to form sheets (lamellastructures) when subjected to stresses inherent in the injectionprocess. However, if the melt flow index of the disperse phase is muchlower than that of the continuous phase the droplets of disperse phasewill tend to resist distortion and not form the lamellar structuredesired for optimum barrier properties. On the other hand, if the meltflow index of the disperse phase is greater than that of the continuousphase it will have a greater tendency to break up under thc sheer stressof mixing thereby leading to a finer dispersion and hence smaller sheersof barrier material, thus reducing barrier performance. It is alsopreferred that the polymer blend, including the barrier polymer, besubjected to no more mixing prior to moulding than is necessary toobtain even mixing. Excessive sheering may result in reduced barrierproperties. The person skilled in the art will be able to determine thedesired amounts of mixing necessary to obtain the optimum balance ofproperties. A further advantage of the formation of these lamellarstructures in polymer blends of the present invention is the ability todesign the mould in order to facilitate flow of the molten polymeracross the mould as well as directly down the core. It is believed thesuch a mould design facilitates biaxial stretching of the barriermaterials to form lamellar structures, which further improve the barrierproperties of the moulded articles.

Another method in which a lamellar/multilayer structure of polymers maybe promoted for use in the present invenrion is by prearrangement of thepolymers of the blend into a composite stream and injecting said streaminto the mould for form articles consisting of largely discrete,generally planar and parallel layers. This may be achieved in a numberof ways, including the coextension of a composite stream of discrete,generally planar and parallel layers of the various polymer componentsof the blends of the present invention, if necessary manipulating thiscomposite stream to form a second composite stream having an increasednumber of layers of substantially uniform thickness, and then directlyinjection moulding the final stream so as to form a multilayer plasticarticle.

In a particularly preferred embodiment of the present invention, thepolymer blend comprises at least one plastomer and at least one ionomer.These polymer blends may advantageously incorporate further polymer toimpart barrier properties to the blend. For example, the incorporationof nylon in such a blend and selecting appropriate blending and mouldingconditions substantially reduces the hydrocarbon and gas permeability ofthe plastomer. The high degree of directional orientation caused by themoulding process is believed to contribute to the imparting of thehighly desirable barrier properties able to be introduced by theaddition of nylon and other essentially incompatible polymers. Nylonitself must be stretched and oriented to form lamellar structures inorder to optimise barrier properties. By incorporating aylon into theblend of plastomer and ionomer the blend may be injection moulded toform components having barrier properties which are believed to havebeen derived from the nylon while retaining resistance to environmentalstress cracking.

While not wishing to be bound by theory, we have found that the at leastone polymer appears to have the property of being able to interact withthe at least one compatible agent whereby he properties of both the atleast one polymer and the at least one compatible agent aresignificantly and unexpectedly changed to enable the polymer blend thusproduced to be suitable for the producdon of thin-walled articles.

It is believed that the interaction between the at least one polymer andthe at least one compatible agent forms regions within the mouldedarticles which can be regarded as “joints”. These “joints” appear toabsorb or disperse stresses in articles made from the polymer blend. Thepresence of these “joints” interspersed within the article appear toabsorb or dissipate the stress which would otherwise result decreasedphysical properties. It is believed that these so called “joints” resultfrom one or more of the following mechanisms:

(i) the polymer and the compatible agent interact, resulting in anincrease in the number of amorphous areas within the polymer;

(ii) the interaction between the polymer and the compatible agentresults in significant localised reduction in crystalliniry, ie.relatively amorphous regions, at the interface between the polymer andthe compatible agent; and

(iii) interaction between the polymer and the compatible agent which,while not resulting in reduced crystallinity and hence more amorphousregions, nevertheless produces a region at the interface between thepolymer and compatible agent which has a greater ability to absorb ordisperse stresses.

In particular it has been found that when the at least one polymer is anethylene homo or copolymer, and preferably a plastomer or substantiallylinear polyethylene, said polymer is able to interact with propylene andmany of its copolymers, and in doing so the crystallinity of saidpolymer is reduced. It is believed that the propylene polymers act ascrystallising agents for the at least one polymer and in doing soincreases the number of amorphous regions within the at least onepolymer. DSC analysis shows that they also act to significantly reducethe overall crystallinity of the ethylene polymer, and particularlyplastomers and substantially linear polyethylene polymers. It is furtherbelieved that these amorphous regions, together with the effects of theinterfaces between the at least one polymer and the propylene polymeract to reduce or disperse the moulded-in stresses in the moulded part,thus increasing its ESCR. At the same ume, salt at least one polymerinteracts with the at least one plastomer or substantially linearpolyethylene and in doing so significantly reduces the crystallinity ofthe at least one plastomer.

It is believed thar many of the polymer blends form a co-continuouslamellar structure and that the interface between the at least onepolymer and the at least one compatible agent is charactensed by anintimate intermingling of the at least one polymer and the at least onecompatible agent at a microscopic level. In other words, it is believedthat the at least one compatible agent acts as an interacting filler. Itis believed that, because of this inrimate intermingling between the atleast one polymer and the at least one compatible agent the overallproperties of the polymer blend are improved. Particularly when lowmolecular weight plastomers and substantially linear polyethylenes arethe at least one polymer, orher polymers previously regarded assubstantially incompatible with polyethylene may now be compatibilisedand blends thereof possess a range of properties which enables thecommercially acceptable production of articles not hithertoforecommercially viable.

It has been found that many compounds known to be capable of nucleatingthe crystallisation of polymers, particularly olefin polymers andcopolymers and especially ethylene polymers and copolymers, improve theESCR properties of polymers for use in the present invention. Dependingon the nature of the individual polymer(s), nucleating agents alone(i.e., without the addition of compatible agents) are capable ofincreasing the ESCR of the polymer(s) to a level that enables saidpolymer(s) to be useful for the manufacture of injection moulded tubes.It is believed that nucleating agents increase the ESCR of polymers intube manufacture by causing the formation of a greater number of smallcrystals than would otherwise be the case. These greater number of smallcrystals result in an increase in the number of amorphous areas withinthe polymer which are capable of absorbing or dispersing stressesintroduced into the tube mouldings during injection moulding—thusincreasing the ESCR and flex resistance of the product. Suitablenucleating compounds for use in tube manufacture include inorganiccompounds such as talc, mica, compounds of various metals such as oxidesand silicate as well as various organic compounds, including variousdyes and pigments. However, for the most beneficial results wheninjection moulding tubes it is preferred that nucleating agents are usedin conjunction with compatible polymers.

It has been found that compounds known to be capable of reducing theglass transition temperature (T_(g)) of the at least one polymer of thepresent invention, particularly olefin polymers and copolymers andespecially ethylene polymers and copolymers, improve r the ESCRproperties of polymers for use in the present invention. Depending onthe nature of the individual polymer(s), T_(g)-reducing agents alone(ie. without the addition of compatible agents, nucleating agents or“high thermal density agents”) are capable of increasing the ESCR of thepolymers) to a level that enables said polymer(s) to be useful for themanufacture of injection moulded tubes. It is believed thatT_(g)-reducing agents increase the ESCR of polymers in tube manufactureby effectively increasing the time that the polymer takes to coll downto its crystalline state, thus increasing the amount of time availablefor the polymer molecules to rearrange themselves so as to reduce themoulded-in stresses. This results in the moulded part having lowermoulded-in stresses than would the case if its T_(g) had not beenreduced, thus resulting in the moulded product having a better ESCR. Asuitable T_(g)-reducing agent is polypropylene. However, for the mostbeneficial results when injection moulding tubes it is preferred thatT_(g)-reducing agents are used in conjunction with compatible agents,unless the T_(g)-reducing agent is in itself a compatible agent.

Poly-2-oxazoline compounds and fluoroelastomers are also suitable foruse as compatible polymers. Incorporation of 1-40%, most preferably2-20% of poly-2-oxazoline compounds improves the ESCR of polymers (seeU.S. Pat. No. 4,474,928). These compatible polymers also improve theadhesion of the PE blend to various substrates, which may make themuseful for preparation of the PE for printing or labelling.

Although the improved ESCR effects of additives such as nucleatingagents and T_(g) reducing agents may not be particularly noticeable in‘normal’ mouldings, it is believed that in mouldings such as thin walledtubes—in which the polymer is subjected to fast cooling rates, highinjection speeds, high injection pressures, long, narrow flow paths andradii, (and resultant high levels of induces stresses)—the effects canbe significant even at low levels of additive addition. It has beenfound tbat such additives may improve the ESCR of certain polymers tothe extent that the at least one polymer and sufficient amount ofadditive alone may be suitable for the production of injection moulded.

According to a further embodiment of the present inveneion, the at leaseone compatible agent may be incorporated into the at least one polymer.For instance, a polymer having monomers incorporating compatibilisergroups may be copolymerised with other monomers to form a compatibilisedpolymer. For example, a monomer having a methacrylic acid group may beadded to the polymerisation mixture of the at least one polymer to forma compatibilised plastomer. Alternatively, a compatibiliser group may begrafted onto the polymer. Advantageously, the polymer onto which acombatibiliser group is grafted is a plastomer or a substantially linearpolyethylene.

The polymer blend may be prepared by extrusion of some or all of thecomponents of ehe polymer blend and the resulting chopped extrusion usedin the injection moulding process of the present invention.Alternatively, the polymer blend may be provided in its component formand subjected to mixing before and during the melting of the polymerblend in the present process.

The polymer blend may be melted by any convenient means. It isparticularly convenient that the polymer blend be melted in aconventional injection moulding machine where a screw rotating in aheated barrel both melts the polymer blend and rams the molten polymerblend into the mould. The articles formed from the polymer blend may bereadily removed from the mould by convenient means.

The injection moulding process of the present invention makes itpossible to produce injection moulded articles having surprisingly thinsections while reraining the mechanical properties of the polymer blend.We have found that articles having cross-sections as thin as 0.3 mm to0.7 mm may be injection moulded, such thin walled articles may have thinwalls over 50 mm in length. These articles may be readily producedwithout substantial deterioration of the mechanical properties of theplastics material.

The polymer blends of the present invention which permit the injectionmoulding of articles having thin sections provides a number ofadvantages which have been hithertofore unattainable due to technicalconstraints. These technical constraints are best illustrated in themanufacture of thin walled tubes. These tubes, which are verycommercially important, are extruded and therefore preclude the use ofcontrol and variation in wall thickness to permit the manufacture oftubes having controlled and variable wall thickness. The presentinvention provides for the manufacture of articles having thin sectionswhere the thin sections are capable of controlled and varied thickness.For example, in the embodiment of an injection moulded tube thethickness of the walls of the tube may be varied along its length. Thewall thickness may be greater at the neck of the tube, thereby allowingincreased flexibility towards the tail. The present invention alsoallows the incorporation of embossing onto the thin walls of the tube.The embossing may take the form of corporate logos, trademarks, varioustext, as well as textures or surface finishes such as a leather grain orripples.

A further advantage of the present invention which has been hithertoforeunattainable due to technical constraints is the use of ‘in-mould’labelling for decorating thin-walled tubes. Extruded tubes cannot bedecorated by in-mould labelling, which therefore requires that anylabelling of such tubes be carried out as a separate and expensivemanufacturing operation. Tubes produced by the present invention can bein-mould labelled during the one-step moulding process, thereby avoidingthe separate and expensive additional manufacturing operation. Theplacement of the labels into the cavity can be achieved by a variety ofmeans, including placing the label on the core when the mould is open,closing the mould and transferring the label from the core to the cavityvia a variety of means just prior the injection of the polymer to forman in-mould labelled tube.

A further advantage of the present invention is the ability to apply abarrier sheath to all or part of the core prior to moulding said barriersheath which is transferred to the moulded article during the mouldingprocess to confer improved barrier or other beneficial properties totubes produced by the present invention. A further advantage of thepresent invention is the ability to apply a coating to either or boththe core and cavity of the mould prior to moulding and which issubsequently transferred during the moulding process to relevant surfaceof the moulded article. This process results in a coating to either theexternal or internal surface of the tubes produced by the presentinvention. Such coatings may have a variety of functions, includingdecorative or barrier.

The present invention which enables the injection moulding of thinwalled articles also provides for many variations in the shape andconfiguration of articles which have hithertofore been restricted due totechnical difficulties in manufacturing thin walled articles. Again,with reference to the thin walled tube example a variety of closures,hooks or flaps may be incorporated into the design. Hithertofore theincorporation of such additional components would require separatecomponents to be manufactured and subsequently welded or otherwiseattached to the tubes, adding significantly to the total cost of thetube. In accordance with the present invention, the use of appropriatelytool designs and/or dual injection moulding equipment permits theone-step manufacture of tubes having integral closures, hooks, flaps orother appendages formed from the same or different polymers.

A number of modifications may be made to standard tube tooling tofacilitate the manufacture of unitary tube/appendage mouldings, inparticular unitary tube/closure mouldings. Such unitary tube/closuremouldings can have, if desired. a wide variety of moulded-in hinges(including living hinges), dispensing spouts and other conveniencefeatures either moulded in during the moulding process. In cases wherethe polymer is used to mould the unitary tube/closure is insufficientlystiff to allow for the moulding of a conventional hinge with‘self-closing’ or ‘flip’ mechanism, the hinge itself may be constructedwith a radius. Provided the polymer has sufficient elasticity, theradius combined with the elasticity of the polymer should result in aself-flipping feature for the closure.

An additional advantage of the process of the present invention is thatby enabling the production of tubes with special contours designed toreceive attachments, it enables the relatively inexpensive and easyattachment of convenience features such as self-sealing valves. Atypical tube/self-sealing closure combination consists of at least fourand often five individual components—a two-part tube (tube body andhead/shoulder), a closure body, a self-sealing valve, a retaining devicefor securing the valve to the body and often a protector for the valveto prevent discharge of the contents, particularly during packing anddelivery to retail outlets. The at least three part self-sealing closureis assembled separately and then attached to the tube. The process ofthe present invention permits the production of a one-part tube/valvereceptor/flip-top protector to which the valve and retaining device canbe easily attached. This reduces the number of parts required to beproduced as well as the complexity and number of steps of the assemblyprocess. This significantly reduces the cost of such rube/closures.

In a further embodiment, the use of the at least one compatible polymerin accordance with the present invention permits the manufacture ofarticles such as tubes may have protective or barrier coatings directlyapplied onto the internal and/or external thin walled sections withoutthe need for pretreatment such as corona discharge or flame treatment.For example, the incorporation of polyoxazoline compounds may improvethe adhesion of lacquers and varnishes to the extent of eliminating theneed for such pretreatment. This may be of particular advantage forcontainers for food use or for containing substances which requirespecific coatings for their containment. Alternatively, suitable barrierand other coatings may be applied by conventional means such as dipping,spraying, printing, vapour or vacuum deposition, this latter processbeing particularly useful for the application of especially high barriermaterials such as metallic or non-metallic oxides/nitrides (eg siliconeoxide) or fluorine as well as carbon and/or organic radicals with usefulproperties. In addition, some coatings, such as coatings produced byreaction of the tube polymer with fluorine, may be further reacted withmonomers containing various beneficial functional groups to furtherenhance the properties of the coatings. For example, hydroxyl-containingmonomers may be reacted with a fluoridated polyethylene coating toproduce a hydroxyl-containing coating.

By their nature, tubes have thin, soft and flexible walls. This lack ofrigidity in the moulded tube makes it difficult to eject the mouldedpart from the core of the mould by normal mechanical means common ininjection and compression moulding and processes such as stripper platesand injector pins, without causing potential damage to the mouldings. Afurther disadvantage is the slow ejection rates often necessary tominimise the chances of damage to the tube on ejection.

We have found that using compressed gas to assist with the ejectionminimises the potential for damage to the tube on ejection, and alsoallows for rapid ejection. When the tube has been formed in the mouldcavity and has set sufficiently for the tube to be retrieved from themould cavity, the male and female part of the mould are separated bytelescopically sliding the male core part out of the female part. At thesame time, or subsequently, the moulded tube can be separated byinjecting compressed gas from within the male core part and to allowcompressed air to communicate with the inside surface of the end part ofthe moulded tube, most preferably by lifting the tip of the core off themain section of the core just prior to the injecting of air in order tobreak the seal that often exists between the moulded tube and the coreto facilitate easier removal of the moulded tube. This lifting of thetip as well as pressurisation beneath the end part will enable themoulded tube and the male core part to be separated by relative slidingmovement of the moulded tube over the tip of male core part. To assistseparation, the male core part may have a very slightly tampered outsidesurface, so the diameter of the male core part is greater at the end ofthe tube remote from the end portion.

Also, the outside surface of the male core part may be formed or treatedso as to have a slight degree of surface roughness sufficient to inhibitformation of a vacuum seal between the moulded portion and the male corepart during the introduction of the pressurised gas. That is, the degreeof surface roughness will allow pressurised air to flow along theoutside surface of the make core part and expand the moulded tubeslightly to separate tube from the core.

In a further improvement to assist removal of the moulded part from thecavity, compressed gas can be injected into the mould just prior to orduring the separation of the core from the cavity in such a way that thegas flows between the outer surface of the moulded part and the interiorsurface of the cavity, thus assisting the separation of the moulded partfrom the cavity and its subsequent removal from the cavity while on thecore of the mould.

To assist in the polymer to flow more easily into the cavity to form thethin-walled article during the injection process, a vacuum may beapplied to the cavity just prior to and during the injection of thepolymer. Mould filling may be further assisted by balancing polymer flowwithin the mould by cutting longitudinal and/or lateral grooves ineither or both the core cavity to direct and/or speed said polymer flowto selected areas within the mould.

The present invention also allows the use of expandable cores in themould which facilitates the release of the thin walled article from themould and also allow the production of thin walled containers havingwide sections adjacent the head and shoulder region in a manner hithertonot possible.

The present invention will be further described by the followingnon-limiting examples and drawings.

DESCRIPTION OF THE FIGURES

FIG. 1 is a view of a thin-walled container made from the polymer blendof the present invention.

FIG. 2 is a view of a thin-walled container made from the polymer blendof the present invention.

FIG. 3 is a view of a thin-walled container made from the polymer blendof the present invention.

FIG. 4 is a view of a thin-walled container made from the polymer blendof the present invention.

FIG. 5 is a view of a thin-walled container made from the polymer blendof the present invention incorporating a hook integrally moulded withthe container. The hook may conveniently be replaced with a spreader orother desirable tool of convenience.

FIG. 6 is a view of a thin-walled container made from the polymer blondof the present invention incorporating a flange with a hole adapted tohang the container from a hook or hanger, at a point of sale.

FIG. 7 is a view of a thin-walled container made from the polymer blendof the present invention incorporating a hook adapted to hang thecontainer from a hook or hanger, at a point of sale.

FIG. 8 is a cut away view of a thin-walled container made from thepolymer blend of the present invention incorporating a barrier coatingon the inside of the container.

FIG. 9 is a view of a unitary tube/enclosure.

FIGS. 10(a) and 10(b) are views of a tube with a side-pouch forreceiving item such as product samples, toothbrushes or combs.

FIGS. 11(a)-14 show detail of some support mechanisms for unitarytube/appendages, and in particular, unitary tube/closures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some of the mould design modifications that can be employed to mouldunitary tube/appendage mouldings are illustrated in FIGS. 11(a)-14. Inthese designs:

1. is the runner for molten polymer

2. is a ‘flip-top’ closure hinged lid

3. is a ‘pop’ mushroom valve

4. is a core

5. is a stem for the ‘pop’ valve (3)

6. is a tube side-wall

7. is a living hinge

8. are channels/grooves for enhanced polymer flow to the tube side-walls

9. is a groove for enhanced polymer flow down the side-walls of the tube10(a). is a support locating on the mushroom valve (3)

10(b). is a support shown in a retracted position

11. are support locations on the mushroom valve (3)

12(a). are supports locating on both the core (4) and the mushroom valve(3)

12(b). is a support locating on the side of the core

13. is an extendable core support shown in the extended position

14. is a support location on the female part of the mould

15. is an extendable core support shown in the non-extended position

In cases of unitary tube/appendages where core flexing or lateral coremovement will not occur if the core is unsupported (for example. inlarge diameter tubes made with high MFI materials), FIG. 11(a)illustrates the longitudinal cross-section of a mould with unsupportedcore capable of producing a unitary tube/closure. FIG. 11(b) is asection plan on line X—X of FIG. 11(a), and FIG. 11(b) is an alternativeX—X to Y—Y section on FIG. 11(a). In a further enhancement of the basictool design, the tool may have a split along the X-X₁ (or X-X₂) line sothat the part of the tool defined by X-X₁ (or X-X₂) and Y—Y can beseparated from the part of the tool defined by X—X to Z—Z. It may bereplaced with an alternative X-X₁ (or X-X₂) to Y—Y tool part [see FIG.11(c)] incorporating a different closure design or type to enable themanufacture of a tube with a different closure. The same principle maybe extended to other appendage types. The ability of this general moulddesign to be easily modified by means of ‘change parts’ for the mouldingof tubes with a variety of different attachments also enables, ifdesired and with the appropriate ‘charge parts’, the moulding of tubeswith no attachments-ie. ‘standard’ tubes with ‘head and shoulders’.

In cases of unitary tube/appendage where core flexing is likely to occurif the core is unsupported, a number of designs are capable ofstabilising the core against lateral movement (and hence variable wallthickness) while still permitting the moulding of the unitarytube/appendage.

FIGS. 12(a) and 12(b) illustrate a tool design in which the core isstabilised against flexing by the use of one or more supports which areprojected out from the top of the female half of the mould and pressdown onto the ‘pop’ valve on the core of the male mould during theinjection of the polymer to form the article. Once the polymer has beeninjected to fill the mould, but prior to the shutting off the barrelvalve, the supports are raised to allow polymer to flow into the gapsleft by the supports, thereby ensuring the formation of completedmoulding. 10(a) shows a support located on the ‘pop’ valve of the core,and 10(b) shows the support raised to allow polymer to flow into thegaps left by the raised support. If appropriate, the support may belocated into a ‘support location area’ (11). FIG. 12(b) is a sectionplan on the X—X line, showing a series of location areas for supports onthe pop-valve.

FIG. 13) illustrates a tool design in which the core is stabilisedagainst flexing by the use of one or more supports [12(a) and 12(b)]which project out from the cavity to support the core from the sideduring the injection of the polymer to form the article. An advantage ofsupport 12(b) is that it also pushes the mushroom valve (3) firmly ontothe core (4), thus minimising the chances of it lifting under injectionpressure. Once the polymer has been injected to fill the mould, prior tothe shutting off of the barrel valve, the supports are retracted toallow polymer to flow into the holes left by the supports, therebyensuring the formation of the completed moulding.

FIG. 14) illustrates a tool design in which extendible supports withinthe core are extended and firmly located into the female parr of themould to ‘anchor’ the core against lateral core movement. Once thepolymer has been injected to fill the mould, prior ro the shutting offof the barrel valve, the support is retracted to allow polymer to flowinto the spaces left by the retracted support, thereby ensuring theformation of the completed moulding. A variation of the above mechanismis to project the whole core upwards to locate it into the female partof the mould, and when the polymer has been injected to fill the mould,but prior to shutting off of the barrel valve, the entire core isretracted to allow polymer to flow into the new cavity left by theretracted core, thereby ensuring the formation of the completedmoulding. Another advantage of this arrangement (ie. not locating thecore through the centre of the closure to be formed) is that the centreof the closure is not restricted by locating devices.

This enables the formation of quite complex closures (eg with spouts andmembranes that enable effective ‘cut-off’ of tube contents) as per somemedicine bottles. In a further variation the mould can be designed toallow a very thin film to be formed across the tip of the aperture ofthe closure for ‘tamper evident’ proof.

Among the main advantages of stabilising mechanisms such as are shown inFIGS. 12-14 is that the core supports are located ‘off-centre’ therebyallowing the injection point to be unimpeded in a central location. Thisallows for the formation of ‘centrally suited’ appendages such asapertures and flow control mechanisms that would otherwise need to belocated ‘off-centre’. If ‘off-centre’ positioning of apertures and otherappendages is acceptable or required, central location of the support ispossible via a number of mechanisms, which are well known to thosepractised in the art.

EXAMPLE 1

A polymer blend made from 50% Exact 4038, 20% Catalloy KS059P and 30%Montell 6100P was injection moulded to form a tubular container having abody having the form of a continuous cylinder 35 mm in diameter and 150mm in length and a neck and shoulder portion adapted to receive a screwcap. The thickness of the continuous cylinder varied from 0.8 mmadjacent to the neck and shoulder portion to 0.5 mm at the remote end.The tubular container was found to possess properties suitable for usein, for example, the cosmetics industry.

EXAMPLE 2

A polymer blend made from 60% Exact 4038 and 40% Montell 6100P wasinjection moulded to form a tubular container having a body having theform of a continuous cylinder 35 mm in diameter and 150 mm in length anda neck and shoulder portion adapted to receive a screw cap. Thethickness of the continuous cylinder varied from 0.8 mm adjacent to theneck and shoulder portion to 0.5 mm at the remote end. The tubularcontainer was found to possess properties suitable for use in, forexample, the cosmetics industry.

EXAMPLE 3

A polymer blend made from 24% Exact 4038, 56% Affinity 1350 and 20%Surlyn 9970 was injection moulded to form a tubular container having abody having the form of a continuous cylinder 35 mm in diameter and 150mm in length and a neck and shoulder portion adapted to receive a screwcap. The thickness of the continuous cylinder varied from 0.8 mmadjacent to the neck and shoulder portion to 0.5 mm at the remote end.The tubular container was found to possess properties suitable for usein, for example, the cosmetics industry.

EXAMPLE 4

A polymer blend made from 24% WSM 168 (Orica Australia Pty Ltd), 56%Affinity 1350 and 20% Surlyn 9970 was injection moulded to form atubular container having a body having the form of a continuous cylinder35 mm in diameter and 150 mm in length and a neck and shoulder portionadapted to receive a screw cap. The thickness of the continuous cylindervaried from 0.8 mm adjacent to the neck and shoulder portion to 0.5 mmat the remote end. The tubular container was found to possess propertiessuitable for use in, for example, the cosmetics industry.

The ESCR Test

Six thin sections of injection moulded polymer blend, 0.65 mm thicknesswere used to determine environmental stress crack resistance. Sections10 mm wide are cut transverse to he major direction of flow of thepolymer blend in the mould and are subsequently created with anypost-mould treatments. Each section is bent back on itself and stapled 3mm from the bend. The bent sections are immersed in a 10% Teric N9solution at 50° C. (Teric is a trademark of Orica Australia Pty Ltd).The strips are then regularly checked for signs of cracking. Any sign ofcracking is regarded as a failure. The time at which 50% (3) of thesections have failed is regarded as the time to failure of the polymerblend. The test is concluded after 360 hours if the polymer has yet tofail.

Comparative Example A

Dow Affinity plastomer having a crystallinity of approximately 34% wasinjection moulded and six sections were cut from the mould and subjectedto the ESCR Test. The results are shown in Table 1 below.

EXAMPLE 5 to 7

Dow Affinity plastomer having 34% crystallinity was compounded withpolypropylene ADP 126 (Montell) in amounts identified in Table 1 below.The blends were injection moulded and six sections were cut from themould and the ESCR Tests performed. The results are shown in Table 1below.

TABLE 1 Dow Affinity Polypropylene ADP Example Plastomer 126 ESCR Test(hr) Comparative A 100%  7  8 97.5%  2.5%  30  9  95%  5% 60 10  60% 40%360+

EXAMPLES 8 to 10

Dow Affinity plastomer having approximately 34% crystallinity wascompounded with Surlyn 9970 (Du Pont) in amounts identified in Table 2below. The blends were injection moulded and six sections were cut fromthe mould and the ESCR Tests performed. The results are shown in Table 2below.

TABLE 2 Dow Affinity Example Plastomer Surlyn 9970 DuPont ESCR Test (hr)Comparative A 100%  7  8 97.5%  2.5%  15  9  95%  5% 30 10  70% 30% 360+

EXAMPLE 11

A polymer blend of 80% Dow Affinity (34%),19% nylon B3 (BASF) and 1.2%Surlyn 9970 was blended. The polymer blend was injection moulded andsubjected to the ESCR Test. The polymer blend had an ESCR Test result of360+ hours.

EXAMPLES 12 and 13

A polymer blend of 80% Dow Affinity (approximately 34% crystallinity)and 20% Surlyn 9970 was blended and injection moulded to form athin-walled tube. A second polymer blend of 76% Dow Affinity (24%crystallinity), 20% nylon B3 (BASF) and 4% Surlyn was blended andinjection moulded to form a thin-walled container. The thin-walledcontainers were filled with petrol and sealed. The polymer blendincorporating 20% nylon and 4% Surlyn showed a permeability to petrolapproximately 20 times less than that of the blend containing plastomerand Surlyn only.

EXAMPLE 14

Dow Affinity plastomer having approximately 34% crystallinity wascompounded with TiO₂ in the amount identified in Table 3 below. Theblends were injection moulded and six sections were cut from the mouldand the ESCR Tests performed. The results are shown in Table 3 below.

TABLE 3 Example Dow Affinity 1300 TiO₂ ESCR Test (hr) A 100%   0% 7 B96.5%  3.5% 22

Those skilled in the art will appreciate that the invention describedherein is susceptible to variations and modifications other than thosespecifically described. It is to be understood that the inventionincludes all such variations and modifications which fall within itsspirit and scope. The invention also includes all of the steps,features, compositions and compounds referred to or indicated in thisspecification, individually or collectively, and any and allcombinations of any two or more of said steps or features.

What is claimed is:
 1. A process for the manufacture of flexible,thin-walled articles comprising the steps of: (a) using a polymer blendhaving an ESCR as herein defined greater than 10 hours; (b) melting saidpolymer blend; (c) ramming molten said polymer blend into a mould havinga cavity that produces a thin-walled article having a thin section of 1mm or less in thickness, the thin section being substantially continuousfor greater than 50 mm in a direction of flow of the molten polymerblend in the mould; and (d) removing from the mould the thin-walledarticle formed from the polymer blend.
 2. A process according to claim1, wherein at least one polymer of the polymer blend has an MFIexceeding ten.
 3. A process according to claim 1, wherein at least onepolymer of the polymer blend has an MFI exceeding twenty.
 4. A processaccording to claim 1, wherein at least one polymer of the polymer blendhas an MFI exceeding thirty.
 5. A process according to claim 1, whereinthe polymer blend has an ESCR greater than 100 hours.
 6. A processaccording to claim 1, wherein the polymer blend has an ESCR greater than200 hours.
 7. A process according to claim 1, wherein the polymer blendhas an ESCR greater than 360 hours.
 8. A process according to claim 1,wherein the thin-walled article is a tube.
 9. A thin-walled tubeproduced according to the process of claim
 1. 10. A thin-walled tubeaccording to claim 9, wherein the thin-walled tube is of unitaryconstruction and incorporates an integral closure, said integral closurebeing formed in the mould.
 11. A process for injection moulding aflexible, thin-walled article comprising the steps of: (a) melting apolymer blend having an ESCR as herein defined of greater than 10 hours,said polymer blend comprising at least one polymer and at least one of acompatible agent and a nucleating agent; (b) ramming molten said polymerblend into a mould having a cavity that produces a thin-walled articlehaving a thin section not exceeding 1 mm thickness the thin sectionbeing substantially continuous for greater than 50 mm in a direction offlow of the molten polymer blend in the mould; and (c) removing from themould the thin-walled article formed from the polymer blend.
 12. Aprocess according to claim 11, wherein at least one polymer of thepolymer blend has an MFI exceeding ten.
 13. A process according to claim11, wherein at least one polymer of the polymer blend has an MFIexceeding twenty.
 14. A process according to claim 11, wherein at leastone polymer of the polymer blend has an MFI exceeding thirty.
 15. Aprocess according to claim 11, wherein the at least one polymer isselected from a group consisting of polyethylenes, copolymers ofethylene and at least one unsaturated olefin, plastomers, ‘substantiallylinear’ polyethylenes, branched polyethylenes, polymers and copolymersof ethylene manufactured using metallocene or other catalysts producingcopolymers characterized by super-random distribution of comonomerswithin the polymer chains, polypropylenes, copolymers of propylene andat least one of ethylene and unsaturated olefins, polymers andcopolymers of propylene manufactured using metallocene or othercatalysts producing copolymers characterized by super-randomdistribution of comonomers within the polymer chains, polylactic acidpolymers, silane polymers and mixtures thereof.
 16. A process accordingto claim 11, wherein the at least one compatible agent is selected froma group consisting of ethylene vinyl acetate; ethylene vinyl alcohol;plasticised polyvinyl acetate and polyvinyl alcohol; alkyl carboxylsubstituted polyolefins; copolymers of anhydrides of organic acids;epoxy group containing copolymers; chlorinated polyethylene;ethylene-propylene-butylene etc. copolymers; ultra low density, very lowdensity, low density, medium density and high density polyethylene;polypropylene, polybutylene and copolymers thereof; polyester ethers;polyether-esters; acrylonitrile-methacrylate copolymers; blockcopolymers having styrene end blocks; half esters; amino andalkoxysilane grafted polyethylenes; vinyl addition polymers;styrene-butadiene block copolymers; acid grafted polyolefins; vinylpyrrolidine grafted polyolefins; block copolymers of dihydric monomers;propylene graft unsaturated esters; modified polyolefins comprisingamide, epoxy, hydroxy or C₂-C₆ acyloxy functional groups,polyoxazolines, fluoroelastomers, other polymeric compatibiliserssuitable for use with polyolefins; particles coated with any of theabove; and mixtures thereof.
 17. A process according to claim 11,wherein the at least one nucleating agent is selected from a groupconsisting of talc, mica, compounds of various metals including oxidesand silicates as well as various organic compounds, including variousdyes and pigments.
 18. A process according to claim 11, wherein thethin-walled article is a tube.
 19. A thin-walled tube produced accordingto the process of claim
 11. 20. A thin-walled tube according to claim19, wherein the thin-walled tube is of unitary construction andincorporates an integral closure, said integral closure being formed inthe mould.
 21. A process according to claim 11, wherein the at least onepolymer is polyethylene or a copolymer characterized by super-randomdistribution of comonomers within the polymer chains and the at leastone compatible agent is a polypropylene based polymer.
 22. A processaccording to claim 21, wherein the at least one polymer is a linear,substantially linear or branched polyethylene or a copolymercharacterized by super-random distribution of comonomers within thepolymer chains and the at least one compatible agent is a polypropylenebased polymer.